Aquatic ecosystem is a useful means to explore complex interaction among different species, and data got from this kind of system can be used to re-constructer or bio-remedy damaged ecosystem or explore other planet, such as Mars. To deeply investigate interactions of different species in space environment, we established a closed aquatic ecosystem of 60 milliliter with Chlorella, Euglena and Bulinus. As a major oxygen producer, Euglena was put into the lower chamber. The initial concentration of Euglena was adjusted to 40000 cells per milliliter to avoid damage of high oxygen concentration to other organisms. As a secondary oxygen producer and food provider, Chlorella was put into the upper chamber together with 3 bulinus. The initial concentration of Chlorella was 3.2*105 cells per milliliter. After 17.5 days of duration, the system run well with 1 bulinus alive in the spaceflight group and all kept alive in the ground control.